转载 GridView异步加载内存卡和网络图片

一、主界面代码：

import java.util.ArrayList;
import java.util.List;

import android.app.Activity;
import android.os.Bundle;
import android.widget.GridView;

public class MainActivity extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        GridView gridView=(GridView)findViewById(R.id.gridview);
        List<ImageAndText> list = new ArrayList<ImageAndText>();
        String[] paths=new String[15];
        for(int i=0;i<15;i++){
            int index=i;
            paths[i]="/sdcard/"+String.valueOf(index+1)+".jpg";//自己动手向SD卡添加15张图片，如：1.jpg
        }
        for(int i=0;i<15;i++){
            list.add(new ImageAndText(paths[i], String.valueOf(i)));
        }
        gridView.setAdapter(new ImageAndTextListAdapter(this, list, gridView));
    }
}

二、以下代码是实现异步获取图片的主方法，SoftReference是软引用，是为了更好的为了系统回收变量，重复的URL直接返回已有的资源，实现回调函数，让数据成功后，更新到UI线程。 

import java.io.IOException;
import java.io.InputStream;
import java.lang.ref.SoftReference;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.HashMap;

import android.R.drawable;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.BitmapFactory.Options;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.Drawable;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
import android.widget.ImageView;

public class AsyncImageLoader {

     private HashMap<String, SoftReference<Drawable>> imageCache;
     public AsyncImageLoader() {
             imageCache = new HashMap<String, SoftReference<Drawable>>();
         }

     public Drawable loadDrawable(final String imageUrl, final ImageCallback imageCallback) {
             if (imageCache.containsKey(imageUrl)) {
                 SoftReference<Drawable> softReference = imageCache.get(imageUrl);
                 Drawable drawable = softReference.get();
                 if (drawable != null) {
                     return drawable;
                 }
             }
             final Handler handler = new Handler() {
                 public void handleMessage(Message message) {
                     imageCallback.imageLoaded((Drawable) message.obj, imageUrl);
                 }
             };
             new Thread() {
                 @Override
                 public void run() {
                     Drawable drawable = loadImageFromUrl(imageUrl);
                     imageCache.put(imageUrl, new SoftReference<Drawable>(drawable));
                     Message message = handler.obtainMessage(0, drawable);
                     handler.sendMessage(message);
                 }
             }.start();
             return null;
         }

    public static Drawable loadImageFromUrl(String url) {
//      /**
//       * 加载网络图片
//       */
//            URL m;
//            InputStream i = null;
//            try {
//                m = new URL(url);
//                i = (InputStream) m.getContent();
//            } catch (MalformedURLException e1) {
//                e1.printStackTrace();
//            } catch (IOException e) {
//                e.printStackTrace();
//            }
//            Drawable d = Drawable.createFromStream(i, "src");

        /**
         * 加载内存卡图片
         */
            Options options=new Options();
            options.inSampleSize=2;
            Bitmap bitmap=BitmapFactory.decodeFile(url, options);
            Drawable drawable=new BitmapDrawable(bitmap);
            return drawable;
        }

    public interface ImageCallback {
             public void imageLoaded(Drawable imageDrawable, String imageUrl);

         }
}

三、ImageAndTextListAdapter是实现ListView的Adapter，里面有个技巧就是 imageView.setTag(imageUrl)，setTag是存储数据的，这样是为了保证在回调函数时，listview去更新自己对应 item。

import java.util.List;

import cn.wangmeng.test.AsyncImageLoader.ImageCallback;

import android.app.Activity;
import android.graphics.drawable.Drawable;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.GridView;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;

public class ImageAndTextListAdapter extends ArrayAdapter<ImageAndText> {

        private GridView gridView;
        private AsyncImageLoader asyncImageLoader;
        public ImageAndTextListAdapter(Activity activity, List<ImageAndText> imageAndTexts, GridView gridView1) {
            super(activity, 0, imageAndTexts);
            this.gridView = gridView1;
            asyncImageLoader = new AsyncImageLoader();
        }

        public View getView(int position, View convertView, ViewGroup parent) {
            Activity activity = (Activity) getContext();

            // Inflate the views from XML
            View rowView = convertView;
            ViewCache viewCache;
            if (rowView == null) {
                LayoutInflater inflater = activity.getLayoutInflater();
                rowView = inflater.inflate(R.layout.griditem, null);
                viewCache = new ViewCache(rowView);
                rowView.setTag(viewCache);
            } else {
                viewCache = (ViewCache) rowView.getTag();
            }
            ImageAndText imageAndText = getItem(position);

            // Load the image and set it on the ImageView
            String imageUrl = imageAndText.getImageUrl();
            ImageView imageView = viewCache.getImageView();
            imageView.setTag(imageUrl);
            Drawable cachedImage = asyncImageLoader.loadDrawable(imageUrl, new ImageCallback() {
                public void imageLoaded(Drawable imageDrawable, String imageUrl) {
                    ImageView imageViewByTag = (ImageView) gridView.findViewWithTag(imageUrl);
                    if (imageViewByTag != null) {
                        imageViewByTag.setImageDrawable(imageDrawable);
                    }
                }
            });
            if (cachedImage == null) {
                imageView.setImageResource(R.drawable.icon);
            }else{
                imageView.setImageDrawable(cachedImage);
            }
            // Set the text on the TextView
            TextView textView = viewCache.getTextView();
            textView.setText(imageAndText.getText());
            return rowView;
        }

}

四、2个辅助类：

public class ImageAndText {
        private String imageUrl;
        private String text;

        public ImageAndText(String imageUrl, String text) {
            this.imageUrl = imageUrl;
            this.text = text;
        }
        public String getImageUrl() {
            return imageUrl;
        }
        public String getText() {
            return text;
        }
}

public class ViewCache {

        private View baseView;
        private TextView textView;
        private ImageView imageView;

        public ViewCache(View baseView) {
            this.baseView = baseView;
        }

        public TextView getTextView() {
            if (textView == null) {
                textView = (TextView) baseView.findViewById(R.id.text);
            }
            return textView;
        }

        public ImageView getImageView() {
            if (imageView == null) {
                imageView = (ImageView) baseView.findViewById(R.id.image);
            }
            return imageView;
        }

}

五、Xml配置文件，包括griditem和main：

1griditem：

<?xml version="1.0" encoding="UTF-8"?>
<RelativeLayout
         xmlns:android="http://schemas.android.com/apk/res/android"
         android:layout_height="100dip"
         android:paddingBottom="4dip" android:layout_width="fill_parent">
         <ImageView
               android:id="@+id/image"
               android:layout_height="80dip"
               android:layout_width="80dip"
               android:layout_centerHorizontal="true"
               android:scaleType="centerCrop">
         </ImageView>
         <TextView
               android:id="@+id/text"
               android:layout_width="wrap_content"
               android:layout_height="wrap_content"
               android:layout_below="@+id/image"
               android:layout_centerHorizontal="true"
               >
         </TextView>
</RelativeLayout>

</pre><pre name="code" class="html">2main:

<pre name="code" class="html"><?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="fill_parent"
    android:layout_height="fill_parent">

    <GridView xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/gridview"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:numColumns="4"
    android:verticalSpacing="10dp"
    android:horizontalSpacing="10dp"
    android:columnWidth="80dp"
    android:stretchMode="columnWidth"
    android:gravity="center"
    android:background="#ffffff"
/>
</LinearLayout>

六、大功告成，总结方法。